Thermomechanical modelling of laser surface glazing for H13 tool steel

A two-dimensional thermomechanical finite element (FE) model of laser surface glazing (LSG) has been developed for H13 tool steel. The direct coupling technique of ANSYS 17.2 (APDL) has been utilised to solve the transient thermomechanical process. A H13 tool steel cylindrical cross-section has been modelled for laser power 200 W and 300 W at constant 0.2 mm beam width and 0.15 ms residence time. The model can predict temperature distribution, stress–strain increments in elastic and plastic region with time and space. The crack formation tendency also can be assumed by analysing the von Mises stress in the heat-concentrated zone. Isotropic and kinematic hardening models have been applied separately to predict the after-yield phenomena. At 200 W laser power, the peak surface temperature achieved is 1520 K which is below the melting point (1727 K) of H13 tool steel. For laser power 300 W, the peak surface temperature is 2523 K. Tensile residual stresses on surface have been found after cooling, which are in agreement with literature. Isotropic model shows higher residual stress that increases with laser power. Conversely, kinematic model gives lower residual stress which decreases with laser power. Therefore, both plasticity models could work in LSG for H13 tool steel

Wear performance of TiC/Fe cermet electrical discharge coatings

The tribological behaviours of TiC-based cermet coatings, prepared by electrical discharge coating (EDC) using a semi-sintered TiC tool electrode, have been investigated. The as-deposited coatings exhibited complex microstructures, comprising TiC grains within an Fe matrix, on both high speed steel (HSS) and 304 stainless steel (304-SS) substrates. The wear resistance of TiC/Fe cermet coatings, on both substrate types, increased dramatically (one and two orders of magnitude improvement in specific wear rate), compared to as-polished substrates. Further, EDC cermet coatings on HSS were typically 2–4 times more wear resistant, depending on loading, than those deposited on 304-SS, with wear performance reflecting the composite nature of the coating coupled with the mechanical properties of the substrate. Laser surface treatments used to improve surface integrity of the as-deposited coatings, through elimination of cracks and porosity characteristic of ED coating, acted to increase wear rates for all samples, with the exception of coatings on HSS under conditions of high loading. The general increase of wear rate was attributed to a significant reduction in the proportion of TiC within the ED coatings, after laser treatment, combined with an increase in grain size; whilst improvements to the wear performance of laser treated, cermet coated HSS, under high loading, was attributed to the avoidance of an abrasive wear mechanism

The Effects of Laser Surface Hardening on Microstructural Characteristics and Wear Resistance of AISI H11 Hot Work Tool Steel

The present study deals with the effects of laser surface treatment on microstructure evolution and wear resistance of AISI H11 hot work tool steel in quenched and tempered condition. The most upper laser-affected zone is characterized by re-melted microstructure consisting of dendrite cells with fresh non-tempered martensite, retained austenite and inter-dendritic carbidic network. The subsolidus microstructure just beneath the re-melted zone represents the most laser surface hardened zone consisting of fresh non-tempered martensite with fine and coarse carbides as a result of overheating the original QT substrate microstructure. The highest microhardness values in the range from 775 to 857 HV were measured for the LSH microstructure and the most softened microstructure exhibited the minimum hardness of 530 HV. The laser treated samples showed the improvement of their surface wear resistance by 35%